Mn(III)-Mediated C-H Phosphorylation of Indazoles with Dialkyl Phosphites

Synthetic Methods for Azaheterocyclic Phosphonates and Their Biological Activity: An Update 2004-2024

The increasing importance of azaheterocyclic phosphonates in the agrochemical, synthetic, and medicinal field has provoked an intense search in the development of synthetic routes for obtaining novel members of this family of compounds. This updated review covers methodologies established since 2004, focusing on the synthesis of azaheterocyclic phosphonates, of which the phosphonate moiety is directly substituted onto to the azaheterocyclic structure. Emphasizing recent advances, this review classifies newly developed synthetic approaches according to the ring size and providing information on biological activities whenever available. Furthermore, this review summarizes information on various methods for the formation of C-P bonds, examining sustainable approaches such as the Michaelis-Arbuzov reaction, the Michaelis-Becker reaction, the Pudovik reaction, the Hirao coupling, and the Kabachnik-Fields reaction. After analyzing the biological activities and applications of azaheterocyclic phosphonates investigated in recent years, a predominant focus on the evaluation of these compounds as anticancer agents is evident. Furthermore, emerging applications underline the versatility and potential of these compounds, highlighting the need for continued research on synthetic methods to expand this interesting family.

Cell Voltage-Dependent Structural Dichotomy: Electrochemical C-H Acyloxylation and N-Acylation of 2H-Indazoles

A simple and efficient electrochemical method that utilizes modulation of the cell voltage to cause structural alterations in 2H-indazole is introduced. This method enables the C-3 acyloxylation of 2H-indazole and promotes the transfer of the acyl group from C-3 to N-1, allowing the N-acylation of 2H-indazoles. Additionally, the application of the μ-electro flow reactor was demonstrated, showcasing its effectiveness in achieving gram-scale production of 3x within a short residence time.

Cu-Catalyzed Regioselective C-H Amination of 2H-Indazoles for the Synthesis of Indazole-Containing Indazol-3(2H)-ones

A copper-catalyzed C3 amination of 2H-indazoles with 2H-indazoles and indazol-3(2H)-ones under mild conditions was developed. A series of indazole-containing indazol-3(2H)-one derivatives were produced in moderate to excellent yields. The mechanistic studies suggest that the reactions probably proceed through a radical pathway.

Recent advances in C-H functionalization of 2H-indazoles

2H-Indazoles are one class of the most important nitrogen-containing heterocyclic compounds. The 2H-indazole motif is widely present in bioactive natural products and drug molecules that exhibit distinctive bioactivities. Therefore, much attention has been paid to access diverse 2H-indazole derivatives. Among them, the late-stage functionalization of 2H-indazoles via C-H activation is recognized as an efficient approach for increasing the complexity and diversity of 2H-indazole derivatives. In this review, we summarized recent achievements in the late-stage functionalization of 2H-indazoles, including the C3-functionalization of 2H-indazoles through transition metal-catalyzed C-H activation or a radical pathway, transition metal-catalyzed ortho C2'-H functionalization of 2H-indazoles and remote C-H functionalization at the benzene ring in 2H-indazoles.

Phosphorylation of arenes, heteroarenes, alkenes, carbonyls and imines by dehydrogenative cross-coupling of P(O)-H and P(R)-H

Organophosphorous compounds have recently emerged as a powerful class of compounds with widespread applications, such as in bioactive natural products, pharmaceuticals, agrochemicals and organic materials, and as ligands in catalysis. The preparation of these compounds requires synthetic techniques with novel catalytic systems varying from transition metal, photo- and electrochemical catalysis to transformations without metal catalysts. Over the past few decades, the addition of P-H bonds to alkenes, alkynes, arenes, heteroarenes and other unsaturated substrates in hydrophosphination and other related reactions via the above-mentioned catalytic processes has emerged as an atom economical approach to obtain organophosphorus compounds. In most of the catalytic cycles, the P-H bond is cleaved to yield a phosphorus-based radical, which adds onto the unsaturated substrate followed by reduction of the corresponding radical yielding the product.

Metal-free regioselective C-H amination for the synthesis of pyrazole-containing 2H-indazoles

A general and practical regioselective approach for the C-H amination of 2H-indazoles under transition-metal-free conditions was developed. A series of substrates were tested showing eminent functional group tolerance and affording the C-N functionalization products in good to excellent yields. Mechanism studies revealed that a radical process was involved in this transformation.